Separation

Go forward out of your Railcar and follow Pavel. Lift him up to the pipe. He will go and get caught. Classic Pavel.

Two guards will now come out of the big door down the hall. Hide behind some rubble, then stealth kill them. Move into the big room. There are multiple ways of going through this room. I tried to be stealthy, but failed.

Once all guards in the area are taken care of, go up to the second floor control room to snag a Note (1/2). You can probably lure guards out by getting them to open a door on the ground floor, but I just went Hulk and killed everyone with guns, then jumped off the barrier to get to the other side.

Climb up the ladder, then go into the door. There is a nice man on a cot, so kill him. (However, if you spare him it helps to earn a "good" ending). The same sound effect from Metro 2033 and this game gives an audio cue that you did something (stum a guitar, listen to a conversation, etc) that counts towards an ending.

To the dead man on the cot's left side is another Note (2/2) and some ammo in the box next to it. Walk forward to find a vent on the left with a bright light shining on it (there's a little more ammo in a box on the floor just past it). Crawl into here to trigger a loading screen.